Bassman780

Good day all, I have a bit of a brain buster here.


2007 Suburban 1500 LTZ 4wd 5.3 Gas engine code 3


About 5 weeks ago, my wife was driving home and noticed that the Check Engine light came on and the Oil Pressure gauge was fluctuating between 60 & 90 than pegged to 90. She made it home and I did some research and found that I should replace the Oil Pressure Sending Unit. Replaced the part on Saturday afternoon and I must say what a Pain in the #@&^. Everything seemed OK pressure was within normal range. Sunday morning I changed the oil and filter and the vehicle ran fine.


Monday morning my wife called me in a panic, she said that the Oil pressure gauge was again bouncing around but than went to the low side and the car turned off, when she went to restart it the MIL was on, and there was a message saying Reduced Engine Power.


Towed the car home and hooked up the Scanner and was given the following codes (I have the Innova 3100 OBD2 scanner) P0641 Voltage A circuit/open and P0532 A/C Ref pressure sensor A circuit low input.


I speaking with a friend (Ford Mechanic) he said it sounded like electrical problem. I checked the Harness in the area of the driveshaft (common problem for that area to have a problem) everything seemed OK. Replaced the Sending Unit again and still had a problem where the computer kept the vehicle in Reduced Power Mode.


I continued to have the same problem so I started to trace the 5 volt system by disconnecting each sensor one by one and when I came to disconnect the Sending Unit all codes reset and the vehicle started (it sounded fine and ran ok for the few minutes I allowed it too).


I reattached the connector to the Oil Pressure Sending Unit and the codes came back and the car went into Reduced Power Mode


I was told that I needed to use a OEM Sending unit as there were common issues with aftermarket parts. (I also replaced the Valve Lifter Oil Filter little screen under sending Unit that most of the Dealerships I called had no idea what I was talking about). Well on my 3rd sending unit I decided that I did not have enough stress in my life and apparently put too much force on the cheap part and it snapped off. Now I had no choice but to pull off the Intake.


While the Intake was removed I had a straight shot to the Oil Pressure Sending Unit (replaced with a 4th new one) I also decided that I may have damaged the connector while trying to reconnect it blindly so I purchased a new one and spliced it into the existing harness (I soldered each wire, covered with shrink tubing, and then electrical tape).


I checked all of the electrical connections as I reinstalled the Intake and didn't notice any problems. I also replaced the Oil Filter


Car started after I cleared codes, Oil pressure gauge did not move from zero, engine sounded fine but went right back into the Reduced Power Mode and MIL light came back on. Scanner just came up with P0641


Stumped I joined the subscription service that Innova offers and it said that the #1 verified fix would be to replace the Fuel Pump Control Module (FPCM) called the dealer to order the part and they told me according to my VIN my vehicle does not have that part.


Stumped I went to the car and disconnected the Oil Pressure Sending Unit electrical connector and low and behold the car started again and ran fine.


HELP!!!!

tech2

Your cheap code reader is giving your red herrings. your truck doesn't have a fpcm, its to old. After the dtc reset, have the codes read by a full function scan tool that can read manufacturer dtc and post them here.

Bassman780

Tech2


I do not do this as a profession so I opted to purchase a middle of the road code reader. The Model I purchased does do manufacturer specific codes. I posted the codes that were listed in the enhanced mode they are the same as the General codes.


According to Chev SI the DTC P0641 5-Volt Reference 1 Circuit ECM


when the Oil Pressure Sending Unit is connected it trips the P0641 Voltage A Circuit/Open when I disconnect the Sending unit the vehicle comes out of reduced power mode and starts/runs ok but trips the P0522 Chev current Engine Oil Pressure Sensor/Switch Circuit Low Input


I'm assuming that the problem is definitely electrical and probably in the circuit with the Oil Pressure Sending Unit. I just can't figure out what is related to these three wires

tech2

I have a $200 c reader vi that does all 10modes of obdII...that is miles above anything made by innova.... and mine will still not read certain powertrain dtc that the factory scan tool will.


I'll look into your dtc but at a glance I doubt that an oil pressure dtc would effect anything to cause a reduced power mode. The only thing that comes to mind would be if the oil pressure sensor shares a 5v ref supply with the throttle actuator or app sensor.
I wonder if a p2135 or p1516 is present but your scan tool can't read it.

tech2

this is what I found:
The 5-volt reference 1 bus provides 5 volts to the following sensors:

• The manifold absolute pressure (MAP) sensor
• The fuel tank pressure (FTP) sensor
• The air conditioning (A/C) refrigerant pressure sensor
• The accelerator pedal position (APP) sensor 2
• The engine oil pressure (EOP) sensor
• The camshaft position (CMP) sensor

so it is on the 5 volt ref circuit.
there is a tsb to check for chaffed wires near the front prop shaft for this dtc


the 5volt ref wire is shorted at the oil pressure sensor so you will have to locate the short.

Bassman780

Tech2 thank you so much for looking this stuff up for me. I did check for the chaffed wire harness near the shaft and that was fine.


I did install a new Oil Pressure Sending connector from what I could see everything appeared to be intact (there was approximately 5" of wire coming out or a main branch of the harness. I cut the old connector out and left approximately 2.5" of the original wires. I soldered each wire and covered each with shrink tubing). Reading schematics is defiantly a weak point for me.


So if the problem goes away when I disconnect that connector does that mean the problem is in just those three wires or are they somehow linked to the other components of the 5 volt system.


Could a bad sensor cause the problem or is it just a bad wire somewhere.


Thanks again


Joe

tech2

one wire...the 5volt ref wire to the oil pressure sensor is shorted to grd. So the short would have to be somewhere between the ecm and the oil sensor connector. probably where the wire goes into a series connection to the sensor.


The way to check for this is to:
key off
-disconnect the ecm connector and the sensor connector
-with an ohm meter connect one lead to the sensor 5volt ref wire and the other lead to grd...there should be no continuity or open. if you get a resistance reading the wiring is shorted.

Bassman780

Tech2


Thank you very much for the information. I will give it a try this afternoon and report back what I find.


Joe

Bassman780

I disconnected the ECM and Sensor checked the 5 volt ref wire and did not get any reading on Ohm meter


I'm lost and open to suggestions this is driving me crazy

Thanks again for your help

tech2

actually, thinking about it, it can't be on the 5volt wire if unplugging the connector makes it go away


check the other 2 wires at the connector the same way just to rule them out. I'LL check the diagnostic when I get a chance.